using System;
using System.Collections;
using System.Collections.Generic;
using System.Diagnostics.CodeAnalysis;
using System.Globalization;
using System.Linq;
using System.Reflection;

namespace WebApiServerProject.Areas.HelpPage
{
    /// <summary>
    ///     This class will create an object of a given type and populate it with sample data.
    /// </summary>
    public class ObjectGenerator
    {
        internal const int DefaultCollectionSize = 2;
        private readonly SimpleTypeObjectGenerator SimpleObjectGenerator = new SimpleTypeObjectGenerator();

        /// <summary>
        ///     Generates an object for a given type. The type needs to be public, have a public default constructor and settable
        ///     public properties/fields. Currently it supports the following types:
        ///     Simple types: <see cref="int" />, <see cref="string" />, <see cref="Enum" />, <see cref="DateTime" />,
        ///     <see cref="Uri" />, etc.
        ///     Complex types: POCO types.
        ///     Nullables: <see cref="Nullable{T}" />.
        ///     Arrays: arrays of simple types or complex types.
        ///     Key value pairs: <see cref="KeyValuePair{TKey,TValue}" />
        ///     Tuples: <see cref="Tuple{T1}" />, <see cref="Tuple{T1,T2}" />, etc
        ///     Dictionaries: <see cref="IDictionary{TKey,TValue}" /> or anything deriving from
        ///     <see cref="IDictionary{TKey,TValue}" />.
        ///     Collections: <see cref="IList{T}" />, <see cref="IEnumerable{T}" />, <see cref="ICollection{T}" />,
        ///     <see cref="IList" />, <see cref="IEnumerable" />, <see cref="ICollection" /> or anything deriving from
        ///     <see cref="ICollection{T}" /> or <see cref="IList" />.
        ///     Queryables: <see cref="IQueryable" />, <see cref="IQueryable{T}" />.
        /// </summary>
        /// <param name="type">The type.</param>
        /// <returns>An object of the given type.</returns>
        public object GenerateObject(Type type)
        {
            return GenerateObject(type, new Dictionary<Type, object>());
        }

        [SuppressMessage("Microsoft.Design", "CA1031:DoNotCatchGeneralExceptionTypes",
            Justification = "Here we just want to return null if anything goes wrong.")]
        private object GenerateObject(Type type, Dictionary<Type, object> createdObjectReferences)
        {
            try
            {
                if (SimpleTypeObjectGenerator.CanGenerateObject(type))
                {
                    return SimpleObjectGenerator.GenerateObject(type);
                }

                if (type.IsArray)
                {
                    return GenerateArray(type, DefaultCollectionSize, createdObjectReferences);
                }

                if (type.IsGenericType)
                {
                    return GenerateGenericType(type, DefaultCollectionSize, createdObjectReferences);
                }

                if (type == typeof (IDictionary))
                {
                    return GenerateDictionary(typeof (Hashtable), DefaultCollectionSize, createdObjectReferences);
                }

                if (typeof (IDictionary).IsAssignableFrom(type))
                {
                    return GenerateDictionary(type, DefaultCollectionSize, createdObjectReferences);
                }

                if (type == typeof (IList) ||
                    type == typeof (IEnumerable) ||
                    type == typeof (ICollection))
                {
                    return GenerateCollection(typeof (ArrayList), DefaultCollectionSize, createdObjectReferences);
                }

                if (typeof (IList).IsAssignableFrom(type))
                {
                    return GenerateCollection(type, DefaultCollectionSize, createdObjectReferences);
                }

                if (type == typeof (IQueryable))
                {
                    return GenerateQueryable(type, DefaultCollectionSize, createdObjectReferences);
                }

                if (type.IsEnum)
                {
                    return GenerateEnum(type);
                }

                if (type.IsPublic || type.IsNestedPublic)
                {
                    return GenerateComplexObject(type, createdObjectReferences);
                }
            }
            catch
            {
                // Returns null if anything fails
                return null;
            }

            return null;
        }

        private static object GenerateGenericType(Type type, int collectionSize,
            Dictionary<Type, object> createdObjectReferences)
        {
            Type genericTypeDefinition = type.GetGenericTypeDefinition();
            if (genericTypeDefinition == typeof (Nullable<>))
            {
                return GenerateNullable(type, createdObjectReferences);
            }

            if (genericTypeDefinition == typeof (KeyValuePair<,>))
            {
                return GenerateKeyValuePair(type, createdObjectReferences);
            }

            if (IsTuple(genericTypeDefinition))
            {
                return GenerateTuple(type, createdObjectReferences);
            }

            Type[] genericArguments = type.GetGenericArguments();
            if (genericArguments.Length == 1)
            {
                if (genericTypeDefinition == typeof (IList<>) ||
                    genericTypeDefinition == typeof (IEnumerable<>) ||
                    genericTypeDefinition == typeof (ICollection<>))
                {
                    Type collectionType = typeof (List<>).MakeGenericType(genericArguments);
                    return GenerateCollection(collectionType, collectionSize, createdObjectReferences);
                }

                if (genericTypeDefinition == typeof (IQueryable<>))
                {
                    return GenerateQueryable(type, collectionSize, createdObjectReferences);
                }

                Type closedCollectionType = typeof (ICollection<>).MakeGenericType(genericArguments[0]);
                if (closedCollectionType.IsAssignableFrom(type))
                {
                    return GenerateCollection(type, collectionSize, createdObjectReferences);
                }
            }

            if (genericArguments.Length == 2)
            {
                if (genericTypeDefinition == typeof (IDictionary<,>))
                {
                    Type dictionaryType = typeof (Dictionary<,>).MakeGenericType(genericArguments);
                    return GenerateDictionary(dictionaryType, collectionSize, createdObjectReferences);
                }

                Type closedDictionaryType = typeof (IDictionary<,>).MakeGenericType(genericArguments[0],
                    genericArguments[1]);
                if (closedDictionaryType.IsAssignableFrom(type))
                {
                    return GenerateDictionary(type, collectionSize, createdObjectReferences);
                }
            }

            if (type.IsPublic || type.IsNestedPublic)
            {
                return GenerateComplexObject(type, createdObjectReferences);
            }

            return null;
        }

        private static object GenerateTuple(Type type, Dictionary<Type, object> createdObjectReferences)
        {
            Type[] genericArgs = type.GetGenericArguments();
            var parameterValues = new object[genericArgs.Length];
            bool failedToCreateTuple = true;
            var objectGenerator = new ObjectGenerator();
            for (int i = 0; i < genericArgs.Length; i++)
            {
                parameterValues[i] = objectGenerator.GenerateObject(genericArgs[i], createdObjectReferences);
                failedToCreateTuple &= parameterValues[i] == null;
            }
            if (failedToCreateTuple)
            {
                return null;
            }
            object result = Activator.CreateInstance(type, parameterValues);
            return result;
        }

        private static bool IsTuple(Type genericTypeDefinition)
        {
            return genericTypeDefinition == typeof (Tuple<>) ||
                   genericTypeDefinition == typeof (Tuple<,>) ||
                   genericTypeDefinition == typeof (Tuple<,,>) ||
                   genericTypeDefinition == typeof (Tuple<,,,>) ||
                   genericTypeDefinition == typeof (Tuple<,,,,>) ||
                   genericTypeDefinition == typeof (Tuple<,,,,,>) ||
                   genericTypeDefinition == typeof (Tuple<,,,,,,>) ||
                   genericTypeDefinition == typeof (Tuple<,,,,,,,>);
        }

        private static object GenerateKeyValuePair(Type keyValuePairType,
            Dictionary<Type, object> createdObjectReferences)
        {
            Type[] genericArgs = keyValuePairType.GetGenericArguments();
            Type typeK = genericArgs[0];
            Type typeV = genericArgs[1];
            var objectGenerator = new ObjectGenerator();
            object keyObject = objectGenerator.GenerateObject(typeK, createdObjectReferences);
            object valueObject = objectGenerator.GenerateObject(typeV, createdObjectReferences);
            if (keyObject == null && valueObject == null)
            {
                // Failed to create key and values
                return null;
            }
            object result = Activator.CreateInstance(keyValuePairType, keyObject, valueObject);
            return result;
        }

        private static object GenerateArray(Type arrayType, int size, Dictionary<Type, object> createdObjectReferences)
        {
            Type type = arrayType.GetElementType();
            Array result = Array.CreateInstance(type, size);
            bool areAllElementsNull = true;
            var objectGenerator = new ObjectGenerator();
            for (int i = 0; i < size; i++)
            {
                object element = objectGenerator.GenerateObject(type, createdObjectReferences);
                result.SetValue(element, i);
                areAllElementsNull &= element == null;
            }

            if (areAllElementsNull)
            {
                return null;
            }

            return result;
        }

        private static object GenerateDictionary(Type dictionaryType, int size,
            Dictionary<Type, object> createdObjectReferences)
        {
            Type typeK = typeof (object);
            Type typeV = typeof (object);
            if (dictionaryType.IsGenericType)
            {
                Type[] genericArgs = dictionaryType.GetGenericArguments();
                typeK = genericArgs[0];
                typeV = genericArgs[1];
            }

            object result = Activator.CreateInstance(dictionaryType);
            MethodInfo addMethod = dictionaryType.GetMethod("Add") ?? dictionaryType.GetMethod("TryAdd");
            MethodInfo containsMethod = dictionaryType.GetMethod("Contains") ?? dictionaryType.GetMethod("ContainsKey");
            var objectGenerator = new ObjectGenerator();
            for (int i = 0; i < size; i++)
            {
                object newKey = objectGenerator.GenerateObject(typeK, createdObjectReferences);
                if (newKey == null)
                {
                    // Cannot generate a valid key
                    return null;
                }

                var containsKey = (bool) containsMethod.Invoke(result, new[] {newKey});
                if (!containsKey)
                {
                    object newValue = objectGenerator.GenerateObject(typeV, createdObjectReferences);
                    addMethod.Invoke(result, new[] {newKey, newValue});
                }
            }

            return result;
        }

        private static object GenerateEnum(Type enumType)
        {
            Array possibleValues = Enum.GetValues(enumType);
            if (possibleValues.Length > 0)
            {
                return possibleValues.GetValue(0);
            }
            return null;
        }

        private static object GenerateQueryable(Type queryableType, int size,
            Dictionary<Type, object> createdObjectReferences)
        {
            bool isGeneric = queryableType.IsGenericType;
            object list;
            if (isGeneric)
            {
                Type listType = typeof (List<>).MakeGenericType(queryableType.GetGenericArguments());
                list = GenerateCollection(listType, size, createdObjectReferences);
            }
            else
            {
                list = GenerateArray(typeof (object[]), size, createdObjectReferences);
            }
            if (list == null)
            {
                return null;
            }
            if (isGeneric)
            {
                Type argumentType = typeof (IEnumerable<>).MakeGenericType(queryableType.GetGenericArguments());
                MethodInfo asQueryableMethod = typeof (Queryable).GetMethod("AsQueryable", new[] {argumentType});
                return asQueryableMethod.Invoke(null, new[] {list});
            }

            return ((IEnumerable) list).AsQueryable();
        }

        private static object GenerateCollection(Type collectionType, int size,
            Dictionary<Type, object> createdObjectReferences)
        {
            Type type = collectionType.IsGenericType
                ? collectionType.GetGenericArguments()[0]
                : typeof (object);
            object result = Activator.CreateInstance(collectionType);
            MethodInfo addMethod = collectionType.GetMethod("Add");
            bool areAllElementsNull = true;
            var objectGenerator = new ObjectGenerator();
            for (int i = 0; i < size; i++)
            {
                object element = objectGenerator.GenerateObject(type, createdObjectReferences);
                addMethod.Invoke(result, new[] {element});
                areAllElementsNull &= element == null;
            }

            if (areAllElementsNull)
            {
                return null;
            }

            return result;
        }

        private static object GenerateNullable(Type nullableType, Dictionary<Type, object> createdObjectReferences)
        {
            Type type = nullableType.GetGenericArguments()[0];
            var objectGenerator = new ObjectGenerator();
            return objectGenerator.GenerateObject(type, createdObjectReferences);
        }

        private static object GenerateComplexObject(Type type, Dictionary<Type, object> createdObjectReferences)
        {
            object result = null;

            if (createdObjectReferences.TryGetValue(type, out result))
            {
                // The object has been created already, just return it. This will handle the circular reference case.
                return result;
            }

            if (type.IsValueType)
            {
                result = Activator.CreateInstance(type);
            }
            else
            {
                ConstructorInfo defaultCtor = type.GetConstructor(Type.EmptyTypes);
                if (defaultCtor == null)
                {
                    // Cannot instantiate the type because it doesn't have a default constructor
                    return null;
                }

                result = defaultCtor.Invoke(new object[0]);
            }
            createdObjectReferences.Add(type, result);
            SetPublicProperties(type, result, createdObjectReferences);
            SetPublicFields(type, result, createdObjectReferences);
            return result;
        }

        private static void SetPublicProperties(Type type, object obj, Dictionary<Type, object> createdObjectReferences)
        {
            PropertyInfo[] properties = type.GetProperties(BindingFlags.Public | BindingFlags.Instance);
            var objectGenerator = new ObjectGenerator();
            foreach (PropertyInfo property in properties)
            {
                if (property.CanWrite)
                {
                    object propertyValue = objectGenerator.GenerateObject(property.PropertyType, createdObjectReferences);
                    property.SetValue(obj, propertyValue, null);
                }
            }
        }

        private static void SetPublicFields(Type type, object obj, Dictionary<Type, object> createdObjectReferences)
        {
            FieldInfo[] fields = type.GetFields(BindingFlags.Public | BindingFlags.Instance);
            var objectGenerator = new ObjectGenerator();
            foreach (FieldInfo field in fields)
            {
                object fieldValue = objectGenerator.GenerateObject(field.FieldType, createdObjectReferences);
                field.SetValue(obj, fieldValue);
            }
        }

        private class SimpleTypeObjectGenerator
        {
            private static readonly Dictionary<Type, Func<long, object>> DefaultGenerators = InitializeGenerators();
            private long _index;

            [SuppressMessage("Microsoft.Maintainability", "CA1502:AvoidExcessiveComplexity",
                Justification = "These are simple type factories and cannot be split up.")]
            private static Dictionary<Type, Func<long, object>> InitializeGenerators()
            {
                return new Dictionary<Type, Func<long, object>>
                {
                    {typeof (Boolean), index => true},
                    {typeof (Byte), index => (Byte) 64},
                    {typeof (Char), index => (Char) 65},
                    {typeof (DateTime), index => DateTime.Now},
                    {typeof (DateTimeOffset), index => new DateTimeOffset(DateTime.Now)},
                    {typeof (DBNull), index => DBNull.Value},
                    {typeof (Decimal), index => (Decimal) index},
                    {typeof (Double), index => index + 0.1},
                    {typeof (Guid), index => Guid.NewGuid()},
                    {typeof (Int16), index => (Int16) (index%Int16.MaxValue)},
                    {typeof (Int32), index => (Int32) (index%Int32.MaxValue)},
                    {typeof (Int64), index => index},
                    {typeof (Object), index => new object()},
                    {typeof (SByte), index => (SByte) 64},
                    {typeof (Single), index => (Single) (index + 0.1)},
                    {
                        typeof (String),
                        index => { return String.Format(CultureInfo.CurrentCulture, "sample string {0}", index); }
                    },
                    {
                        typeof (TimeSpan), index => { return TimeSpan.FromTicks(1234567); }
                    },
                    {typeof (UInt16), index => (UInt16) (index%UInt16.MaxValue)},
                    {typeof (UInt32), index => (UInt32) (index%UInt32.MaxValue)},
                    {typeof (UInt64), index => (UInt64) index},
                    {
                        typeof (Uri),
                        index =>
                        {
                            return
                                new Uri(String.Format(CultureInfo.CurrentCulture, "http://webapihelppage{0}.com", index));
                        }
                    },
                };
            }

            public static bool CanGenerateObject(Type type)
            {
                return DefaultGenerators.ContainsKey(type);
            }

            public object GenerateObject(Type type)
            {
                return DefaultGenerators[type](++_index);
            }
        }
    }
}